company where I worked, someone famously (or infamously) did a study on beagles with a drug we were testing that contained methylxanthine, a class of alkaloids that includes caffeine. All you dog owners know the toxicities of caffeine on dogs, but the boob PhD who ran the study apparently didn't do his homework. None of the dogs died fortunately, but they all had adverse reactions and the study was a failure.

I'm hardly an expert, but one of the scientists explained to me that more common and successful testing is in mice and rats (because the effects can be observed and extrapolated generally to other species and because they are inexpensive and plentiful), pigs (which have some remarkable similarities to human physiology), and monkeys (for the same reason, but typically for later stage studies because they are expensive and require more skill to work with). Early safety and efficacy trials typically stick with mice and rats. Our company would not typically move on to more complex animals unless we were pretty sure we had a promising clinical candidate.